Hybrid powertrains may improve vehicle fuel economy in a variety of ways. For instance, in some hybrid powertrains, the engine may be turned off at idle, during periods of deceleration and braking, and during periods of low speed or light load operation to eliminate efficiency losses due to engine drag. Tractive torque for propulsion is provided only by one or more motor/generators in an electric-only operating mode. The motor/generators are able to capture vehicle kinetic energy during braking, which is used to keep the engine off longer, supplement engine torque or power and/or operate at a lower engine speed, or supplement accessory power supplies. Additionally, the motor/generators are very efficient in accessory power generation and electric power from the battery serves as an available torque reserve allowing operation at a relatively low transmission numerical speed ratio. The hybrid powertrain must be designed to perform when vehicle operating conditions require high output torque. Relying on torque from the motor/generators to do so may necessitate the use of relatively large motor/generators and/or a large energy storage device.